dcpatti is right on the money as the big issue with doing OLCI with an infant is that they can't verify the infant's age. What some people have done in the past is some how get a FF account for their infant so they can then make use of the OLCI feature once their birthday is in their record.
I've read about several different situations with the 10% infant charge on international flights. Many airlines charge 10% of the highest applicable fare in the class you're travelling in, and if you upgrade they will charge you the difference in fare with a change of cabin at the airport. Others have said that they were initially charged a reduced 10% and not charged the difference when the cabin changed. Looks like YMMV in this one, unless you can get someone in res to give you a specific answer in writing that you can carry with you.